1. Technical Field
The present invention relates to forward error correction (FEC) for high-speed serial optical transport and, in particular, to systems and methods for FEC encoding with low density parity check codes based on a modified progressive edge growth (MPEG) method.
2. Description of the Related Art
In the recent years, with the rapid growth of data-centric services and the general deployment of broadband access networks, the dense wavelength division multiplexing (DWDM) network has been upgraded from 10 Gb/s per channel to more spectrally-efficient 40 Gb/s or 100 Gb/s per channel systems and beyond. 100 Gb/s Ethernet (100 GbE) is currently under standardization for both local area networks (LANs) and wide area networks (WANs). As the communication rate over a given medium increases, transmission becomes increasingly sensitive to errors due to various linear and nonlinear channel impairments such as chromatic dispersion, PMD and fiber nonlinearities. The Shannon limit for a noise-influenced channel describes a maximum amount of error-free data that can be transmitted with a specified bandwidth—it is therefore helpful to have robust codes and modulation schemes that closely approach the Shannon limit without imposing high requirements in terms of implementation cost and complexity.
Random low-density parity-check (LDPC) codes provide excellent error-correcting capabilities, but they are difficult to implement because of the lack of mathematical structure in their parity check matrices. Meanwhile, quasi-cyclic (QC) LDPC codes are easy to implement, but this comes at the expense of performance. To ameliorate the performance loss of structured LDPC codes, girth (the shortest cycle in the LDPC code parity check matrix's corresponding bipartite graph) is used as an optimization parameter. Large-girth QC-LDPC codes provide good bit-error rate (BER) performance, but require excessive codeword length for girths higher than 8.